This invention relates to emulsion copolymers and their use for the thickening of a variety of aqueous systems, to methods of thickening utilizing the copolymers, to enhancement of such thickening by the addition of surfactants, and to other aspects including coating compositions and other aqueous systems thickened with the polymers.
This application is related to applicant's Ser. No. 101,615, filed Dec. 10, 1979, and corresponding to European Patent Publication No. 13,836, dated Aug. 6, 1980, entitled "(Meth)acrylic Acid Emulsion Copolymers for Thickening Purposes". This earlier application discloses emulsion copolymers, and the use thereof as thickeners in aqueous dispersions, of (meth)acrylic acid, an alkyl poly(oxyethylene) (meth)acrylate, and a C.sub.1 -C.sub.4 alkyl (meth)acrylate, and, optionally, a small amount of a polyethylenically unsaturated monomer.
European Patent Publication No. 11,806, dated June 11, 1980, discloses aqueous emulsion polymers which are pH responsive and are prepared by emulsion polymerization of 15-60% of an .alpha.,.beta.-ethylenically unsaturated carboxylic acid, 15-80% of an .alpha.,.beta.-ethylenically unsaturated monomer, and 1-30% of a nonionic vinyl surfactant ester, preferably a monovinyl ester such as nonyl phenoxy poly(ethyleneoxy).sub.9 ethyl acrylate.
U.S. Pat. No. 4,138,381 discloses a liquid composition useful as a thickening agent in polymeric latices of (A) 50 weight percent of a polymer of units of (1) 10-98% of an unsaturated C.sub.3 -C.sub.6 carboxylic acid, (2) about 1-50% of a C.sub.1 -C.sub.30 alkyl (meth)acrylate, and (3) 1-18% of an ester of the formula: ##STR1## where x is 5-80, y is 0-20, R and R.sup.2 are H or CH.sub.3, and R.sup.1 is alkyl or phenyl; and (B) as a solvent for (A), (4) a glycol, or (5) a glycol containing up to 50% of its weight of water; the composition being made by free radical solution polymerization techniques.
U.S. Pat. No. 4,268,631 discloses a normally solid, base-neutralized copolymer having copolymerized therein about 90-99 mole percent of a carboxyl-containing ethylenically unsaturated hydrocarbon and about 1-10 mole percent of a nonionic surfactant acrylate having the formula: EQU R.sup.1 --(A).sub.x --OC(O)--CR.dbd.CH.sub.2
wherein R is H or CH.sub.3, R.sup.1 is a hydrophobe selected from the group consisting of alkyl--O--, alkyl--CH--, and alkyl--CO--, where alkyl contains 4-30 carbon atoms, A is a divalent radical selected from the group consisting of oxyethylene or oxyalkylene units or mixed oxyalkylene units --OC.sub.n H.sub.2n) where n is an integer from 2 to 4 and x is an integer of 5-40, said surfactant acrylate having an HLB (hydrophilic lipophilic balance) value of about 10-19.
Salts of polyacrylic acid and polymethacrylic acid are well known as thickeners for various aqueous systems. A polyacrylic acid obtained by copolymerizing acrylic acid with a small amount (about 0.2 to 1% by weight on the weight of acrylic acid) of diallyl sucrose (U.S. Pat. No. 2,798,053) has also been sold for use as a thickener for many years. These thickening agents are difficult to handle because they are either powders that are slow to dissolve or very viscous aqueous solutions. Adverse effects such as stiffness or water sensitivity also may be imparted to the finished product by the polymeric acid thickener. Still another problem associated with the acid thickeners is their electrolyte sensitivity. The aqueous systems thickened with these thickeners decrease drastically in viscosity upon addition of an electrolyte, such as sodium chloride.
British Pat. No. 870,994 discloses the preparation of aqueous emulsion copolymers of methacrylic acid and a lower (C.sub.1 -C.sub.4) alkyl acrylate which gives good thickening upon neutralization. The copolymer dispersions having a solids concentration of 25 to 50% by weight are low viscosity fluids and are thus readily added directly to systems to be thickened. However, they also have severe electrolyte sensitivity.
These polyelectrolyte polymers are useful as bodying and suspending agents in various mucilaginous and colloidal gel-like applications such as dentrifices, surgical jellies, creams and ointments, printing paste thickeners, and the like. However, most polyelectrolyte solutions decrease drastically in viscosity upon the addition of electrolytes such as sodium chloride. These prior art thickener materials are ion-sensitive and do not adequately maintain the viscosities of water or organic solvent solutions containing inorganic salts such as sodium chloride, even when a third monomer such as 2-ethylhexylacrylate or styrene, respectively, is included in the polymer as is suggested by the respective prior art patents.